On the adsorption mechanism of caffeine on MAPbI₃ perovskite surfaces: a combined UMC-DFT study

Recently, it was experimentally shown that the performance and thermal stability of the perovskite MAPbI₃ were improved upon the adsorption of a molecular layer of caffeine. In this work, we used a hybrid methodology that combines uncoupled monte carlo (UMC) and density functional theory (DFT) simulations to carry out a detailed and comprehensive study of the adsorption mechanism of a caffeine molecule on the surface of MAPbI₃. Our results showed that the adsorption distance and energy of a caffeine molecule on the MAPbI₃ surface are 2.0 Å and -0.3 eV, respectively. The caffeine/MAPbI₃ complex presents a direct bandgap of 2.38 eV with two flat intragap bands distanced 1.15 and 2.18 eV from the top of valence bands. Although the energy band levels are not significantly shifted by the presence of caffeine, the interaction MAPbI₃/perovskite is enough to affect the bands' dispersion, particularly the conduction bands.